The present invention relates to an apparatus for providing continuity of operation in a computer, and in particular to providing continuity of operation in a small-sized computer by utilizing an external storage element.
Continuity for personal computers as used herein constitutes the turning on and off of a personal computer power supply such that when the power supply is again turned on, the system state is restored to the condition existing when the power supply was last turned off. Thus, permitting the continuation of processing being executed prior to the turning off of the power supply. The need for continuation has increased with the advent of small-sized, battery driven computers. These portable computers can be used irrespective of places and times for operation. For example, they may be utilized while waiting for trains or airplanes or during free time before the start of meetings. Often, it is difficult to complete all of the required processing procedures in such a limited time period. Accordingly, it often becomes necessary to shut down the computer in the middle of an operation. On these occasions, portable computers would become more convenient to use if the suspended processing can be continued later at any time after turning off the computer power supply.
Small-sized computers are generally powered by a rechargeable battery source. Therefore, if the battery voltage becomes too low (hereinafter referred to as "low battery") during periods of use or when a power switch is left turned on due to inadvertence of the user, the current computer processing should be suspended during a low voltage situation and then resumed later after recharging. In a worst case, if computer processing is not suspended then all of the data would be lost during the power supply cut-off. Also in such cases, it would be advantageous to turn off the power supply in a current saving state, and then resume the suspended processing once the low battery state has been remedied.
As seen above, computing continuity is crucial for convenient use of portable computers. Realization of continuity absolutely requires that the system state at the point when the power supply was last turned off be maintained. The system state includes the contents of a main memory, the setting conditions of input/output (herein after "I/O") ports, the state of the central processing unit (hereinafter "CPU") and the like. The setting conditions or status of the I/O ports in turn specify the computer hardware conditions at the time of turn-off of the power supply. The hardware conditions can be stored as information in the main memory and therefore, can be considered as retention of data in the main memory.
With conventional computers retention of data in the main memory has been realized by providing a power supply backup for the main memory. Specifically, the memory means includes a static RAM (hereinafter "SRAM") and power is continuously supplied to the main memory even after the power supply has been turned off to retain the content of the SRAM. If the memory means includes a dynamic RAM (hereinafter "DRAM"), power is supplied to periodically refresh the main memory even after the power supply has been turned off.
The conventional small computers have been satisfactory. However, those continuity structures suffer from the disadvantage that the system cost increases due to the increased complexity of the backup power supply circuit configuration as well as the specialized design of devices employed.
Additionally, because even the backup power source requires batteries the data cannot be preserved over a long time period without recharging the batteries. Thus the resulting system is expensive, and does not accomplish continuity over a long time period.
Accordingly, it is desired to provide an apparatus for providing continuity of operation in a computer which overcomes the disadvantages of the prior art device described by providing an external recording structure independent of the computer power source.